1. Characteristics and status of the cupola
The cupola is a kind of vertical tube melting smelting equipment which uses coke combustion as a heat source, and is mainly used for melting cast iron materials with carbon content of 2.2% or more. It can smelt various grades of gray cast iron, ductile iron, malleable cast iron and medium and low alloy cast iron. Compared with other heat source melting furnaces, the combustion of coke in the cupola, the melting of the charge, and the overheating are carried out in the mutual contact of metal, coke and furnace gas. The maximum temperature in the furnace can exceed 1800 °C, forming the best heat transfer conditions and metallurgical environment. The high temperature in the furnace can overcome the poor genetic characteristics of the metal charge. The high melting point oxide formed by the high temperature metallurgical reaction can become the molten iron. The heterogeneous crystal nucleus enhances the graphitization ability of the molten iron, and the impurities and gases in the molten iron are eliminated along with the metallurgical reaction and the formation of the slag, and the casting cast by the cupola molten iron has good mechanical processing properties.
Cupola also has continuous smelting, small one-time investment, technical transformation is not limited by power supply, construction speed is fast, operation and maintenance is simple, and there is no electromagnetic pollution.
At present, the annual output of China's cast iron parts has reached 20 million tons, cupola furnace smelting accounted for more than 80%, there are more than 20,000 cupolas in active service, the average annual output is less than 1000 tons, and the cupola with melting rate of 1-3T/h can be seen. Still the vast majority.
2. History of the development of cupola in China
In the early days of the founding of China, China's cast iron smelting still uses the traditional scoop furnace (also known as the furnace, which began in the Yuan Dynasty). The furnace uses a single eye, consisting of a bottom basin for iron and a top section for coke and iron. The advantage is that the molten iron is highly visible, there is no need to block the molten iron operation, and the furnace body is inclined to iron. The disadvantage is that the effective height is insufficient, the thermal efficiency is low, and the amount of molten iron in the bottom basin is too small. The bottom basin of the scoop furnace is raised and fixed on the ground, and then a section is added to the furnace body on the scoop furnace to form a three-section furnace. The thermal efficiency is improved compared with the scoop furnace, and the iron content of the bottom basin is improved. The amount is increased, which can meet the production needs of some low-grade and heavy-weight cast iron parts.
It was not until 1954 that a three-row large-window cupola (25% of the tuyere) with modern significance was introduced from the former Soviet Union. However, the coke used in the domestic cupola was mainly metallurgical coke and a large amount of soil coke. The degree is small, the ash is large, and the fixed carbon content is low. The large ventilating cupola is often forced to shut down because of the coking of the tuyere (the vent is black), and the average tapping temperature is only 1350 ° C ~ 1380 ° C.
From 1958 to 1965, the vast number of foundry workers in China concentrated almost all the intensive smelting measures that could be taken on the cupola, and launched a multi-row small-wind ribbed hot air bile cupola, which narrowed the tuyere. The wind speed of the furnace is increased, the hot air temperature is close to 200 °C, and the combustion environment of the bottom coke is improved. The ratio of coke to iron is 1:17 to 1:18, and the temperature of molten iron is stable at 1350 °C to 1380 °C, but the furnace is silicon and manganese. Burning loss is greater than 30%.
In 1979, a factory in Hubei was the first to create a card waist cupola. This type of furnace uses two rows of short-pitch and high-angle air outlets. The main air outlet is placed in the second row, and the waist is formed above the second row of air outlets. 1T/h test furnace test results, the ratio of coke to iron is 1:10, the temperature of molten iron is greater than 1490 ° C, the loss of silicon burning is less than 8%, and the burning of manganese is 12%. This is a cupola with less burning of alloying elements and high temperature of molten iron. Once it appeared, it caused great interest in the casting industry. However, the waist of the card waist furnace repaired with refractory material is in the oxidation zone, where the furnace gas temperature is the highest, the burning speed is fast, and the time for maintaining the high temperature card furnace is very short.
In 1984, the Shenyang Foundry Research Institute organized relevant research institutes to carry out experimental stereotypes on two rows of large-space cupolas. In 1987, it passed the appraisal of the former Ministry of Machinery and Electronics Industry. There are two oxidation zones in the two rows of large-pitch cupola. The two reduction zones have a long overheating distance. When the ratio of coke to iron is 1:7, the temperature of molten iron is greater than 1450 °C, the loss of silicon is less than 20%, and the loss of manganese is less than 25%.
In 1993, a factory in Jiangyin developed the first cold-cooled cupola furnace with a large-winding double-row air supply and a long furnace in China on the basis of two rows of large-distance cupolas. The furnace age can reach four weeks. The extension of the water-cooled cupola furnace age is at the cost of the heat taken away by the cooling water. It is only suitable for cupolas above 5T/h.
3. Development of combined cupola
From the above history of the development of China's cupola, it can be clearly seen that the succession of various cupolas in the chain of time, the cupola that appeared later has retained some of the advantages of the cupola. Then, can we put forward the advantages of various cupolas one by one, recombine, and create a new cupola? The answer is yes - we did it - that is the combined cupola.
To measure the quality of the cupola, I personally think it should be "high temperature, high quality, low consumption, and environmental protection." High temperature means that the temperature of molten iron is high; high quality means that the content of molten iron is low and the purity is high; low consumption means low consumption of coke; environmental protection means that the flue gas purification equipment can be conveniently connected, and the power consumption is less. How can we achieve the above goals? It is necessary to make a breakthrough in theory. The cupola is actually a large heat exchanger. It is the direct heat exchange between the furnace gas and the hot coke and the metal charge. The heat transfer effect depends on the maximum temperature that the furnace gas can reach. , the flow rate of the furnace gas, the contact time of the furnace gas and the metal charge. An important reason why a good cupola can be accepted by users is whether the operation is simple, the maintenance is convenient, and more importantly, the boss has to save money. Based on the above facts, we carried out the re-creation of the cupola.
The combined cupola keeps the high temperature of the scoop furnace visible and does not need to block the operation of the iron mouth. At the same time, it uses a unique partition to separate the coke from the molten iron in the bottom basin, avoiding the scoop coke soaking in the molten iron. The carbon-increasing and sulfur-increasing process eliminates the long handle of the scoop furnace and replaces it with a rack mechanism with a reduction gear box, so that when the iron is tapped, the iron can be poured out simply by turning the hand wheel, like pouring iron from the ladle Convenience. The curved hearth of the multi-row small air vent is retained, and the relevant proportion of the curved furnace is further adjusted to make the melting zone more straight. It absorbs the beneficial effect of the hot air of the dense rib furnace, adopts the overall thin furnace lining air-cooling structure, minimizes the contact area between the furnace and the furnace gas, and has a hot air of more than 200 °C when the iron is discharged. The traditional ribs are doubled. Retain the two rows of short-pitch and high-angle air outlets in the waist furnace to further enhance the burning of the bottom coke, and appropriately reduce the amount of bottom coke added. It is proved by data that the amount of molten iron spheroidizing agent in the combined cupola melting is higher than that of the traditional cupola. The furnace is 0.5% less. Since our combined cupola is designed for users of 0.5~3T/h, the furnace body is divided into five sections for the convenience of repairing the furnace. When the furnace is repaired, many people can work at the same time, which changes the traditional cupola "wet mud". The method of repairing the furnace, the severe melting zone is the same as that of the intermediate frequency electric furnace, and is made of refractory material. Using the cheap refractory formula developed by our factory, the hourly burning rate of the furnace wall can be less than 8mm. Due to the large reduction of the falling off of the furnace wall, the amount of slag of the combined cupola is only one third of the traditional cupola. In the combined cupola, when the fixed carbon is greater than 83%, the layer coke ratio is 10:1, the molten iron temperature is greater than 1450 ° C, the silicon burning loss is less than 10%, and the manganese burning loss is less than 15%.
The combined cupola was successfully developed in 2006. In the same year, it won the national patent (patent number: ZL200620005051.4), and in 2010 it won the national patent (patent number).
The following two field furnace records are reported to the peers:
A factory in Hebei on January 8, 2008 (2T/h)
The refractory materials for the furnace are as follows: 100 pieces of clay refractory bricks (45-65)×230 knives, 120 pieces of 65×230 ​​standard bricks, 100 pieces of 30×230 thin bricks, 200kg of quartz sand, and 270kg of refractory soil. After the furnace is built, the charcoal ignited by the wood is baked for 20 hours to completely dry the furnace wall. After loading the lead material, put a hopper coke (65Kg), 11:25 points, ignite with oxygen acetylene cutting torch, 13:10 points, the exhaust eyes are already bright, plus two hopper coke, the last batch of 4 batches, each The batch material is 40Kg iron, 30Kg recycled material, 30Kg scrap steel, 0.5Kg ferrosilicon, 1Kg ferromanganese, 10Kg coke, and 2Kg limestone. 13:25 minutes of air supply, 10 minutes after the iron flower fly out, 14:00 a pack of molten iron, the average melting rate per hour 2.1T, hot air temperature 200 ° C, measured iron temperature 2 times, 1470 ° C, 1490 ° C, the same day Smelting molten iron 11T.
A factory in Shandong on February 23, 2009 (3T/h)
Add bottom weight 3 flat hopper (85Kg per bucket), after 8 minutes of air supply, there is iron flower floating out of the cold iron mouth, which will flow quickly and the temperature is very high. Plug the cold iron mouth and start normal melting. The batch of material is batched for 3 minutes. Each batch is 75Kg iron, 75Kg recycled material, 15Kg coke, 2Kg limestone, and 10Kg of carbon in every 10 batches. 30 minutes of lunch break, combined with the wind and the wind, the normal air supply after work in the afternoon, avoiding the danger of blocking the bridge. The material should be stopped half an hour before the furnace is pulled. When the material level drops to the first section interface, the wind shield is combined with the wind release, so that the upper mouth of the furnace has a slight flame. The hot air temperature is 210 ° C at the beginning and 260 ° C at the later stage. The temperature of the molten iron is 1510. °C, a total of 8 hours of furnace opening, 20.5T of iron, because 3T is too fast per hour, does not match the production cycle, using wind-shielding operation.
About the author: Zhao Wenhe (1967), male, Hailin City, Heilongjiang Province, foundry engineer, has long been engaged in cupola research, has a number of national patents, and is currently the chief engineer of Hailin Jiujiu Industrial Furnace Manufacturing Plant. phone
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